| Inkyspider Limited | Information & communication | 2017 |
| Inline Ortho Limited | Health & social care | 2014 |
| Inner City Maintenance Limited | Other services | 2024 |
| Inner North Ltd | Education | 2025 |
| Innolight Ltd | Construction | 2018 |
| Innovation Performance Technologies Ltd | Education | 2022 |
| Innovation Systems & Design Limited | Manufacturing | 2004 |
| Innovensa Limited | Information & communication | 2017 |
| INQ Technologies Limited | Information & communication | 2019 |
| Insight Cardiovascular Limited | Health & social care | 2026 |
| Inspector Drain Services Ltd | Construction | 2025 |
| Inspirational Education Consultancy Ltd | Education | 2012 |
| Inspire Group Investments Limited | Professional & scientific | 2010 |
| Inspired Home Developments Ltd | Construction | 2023 |
| Inspirex Limited | Information & communication | 2009 |
| Inssein Ltd | Other services | 2022 |
| Intec IOT Limited | Information & communication | 2022 |
| Integra EDU Ltd | Arts & recreation | 2020 |
| Integra PT Ltd | Arts & recreation | 2020 |
| Integrail Limited | Construction | 2013 |
| Integral Moving Services Ltd | Transport & logistics | 2013 |
| Integrated Business Telecommunications Limited | Information & communication | 2003 |
| Integrated Computer Services Ltd | Extraterritorial | 2017 |
| Integrated Project Initiatives Ltd | Professional & scientific | 2011 |
| Inteligenyx Limited | Administrative & support | 2025 |
| Intelligent Lighting Support Ltd | Professional & scientific | 2009 |
| Interesting Picture Company (GB) Limited | Information & communication | 2018 |
| Interhous Limited | Professional & scientific | 2019 |
| Interior Choice Limited | Administrative & support | 2011 |
| International Postal Communications Limited | Administrative & support | 2005 |
| Interpreter International Limited | Information & communication | 2025 |
| Intertrade Solutions Limited | Professional & scientific | 2002 |
| Intevolve Limited | Information & communication | 2025 |
| Intospass - International Outer Space Association Ltd | Manufacturing | 2023 |
| Intralex Limited | Professional & scientific | 2004 |
| Intrepid INK Limited | Arts & recreation | 2019 |
| Intrio Ltd | Information & communication | 2024 |
| Investdid Ltd | Other services | 2023 |
| Investicase Ltd | Administrative & support | 2025 |
| Invis-Ability C.I.C. | Education | 2018 |
| Invo Consulting Limited | Information & communication | 2021 |
| Ionut Burlacu Ltd | Construction | 2014 |
| IPM Property Services Limited | Administrative & support | 2009 |
| IQ Eggs Limited | Agriculture & fishing | 2009 |
| Irekcom Limited | Transport & logistics | 2023 |
| IRI UK Transport Ltd | Administrative & support | 2025 |
| Irish Film and Television UK Ltd | Information & communication | 2012 |
| Iron Lion Films Limited | Information & communication | 2010 |
| Iron Stone Healthcare Ltd | Health & social care | 2023 |
| Ironline Fencing Ltd | Construction | 2026 |
| Ironworks Services Limited | Professional & scientific | 2025 |
| Irrigation Solutions Ltd | Construction | 2025 |
| Irwin Court Management Company Limited | Households | 1995 |
| IS Austin Consultancy Limited | Administrative & support | 2013 |
| Isabella Place One (Chafford Hundred) Management Company Limited | Households | 2003 |
| ISH Drylining Limited | Construction | 2024 |
| Ishaadi Ltd | Information & communication | 2016 |
| Ishu Counselling Services Ltd | Professional & scientific | 2024 |
| Islington Investments Ltd | Real estate | 2005 |
| Islington Property Group Limited | Real estate | 2022 |
| Ismedia Production Ltd. | Manufacturing | 2021 |
| Ismosys Group Limited | Wholesale & retail | 2021 |
| Isoform Oncology Ltd | Professional & scientific | 2024 |
| Ispas Installations Ltd | Construction | 2015 |
| Ispf Holdings Limited | Financial services | 2025 |
| Ispf Pipework Limited | Construction | 2022 |
| Isqueeze Limited | Wholesale & retail | 2011 |
| IT (Herts) Limited | Other services | 2010 |
| IT Brokers Ltd | Information & communication | 2017 |
| Itdaas Ltd | Administrative & support | 2020 |
| Itexs - Telecom Ltd | Information & communication | 2013 |
| Itexs Limited | Information & communication | 2002 |
| Itica Limited | Professional & scientific | 2004 |
| Iuorty Ltd | Manufacturing | 2026 |
| IVC Civil Ltd | Construction | 2024 |
| IWL Contractors Limited | Construction | 2011 |
| Iykeman Solutions Ltd | Wholesale & retail | 2018 |
| Iyra Health Ltd | Health & social care | 2024 |
| J & B Homestyles Limited | | 1983 |
| J & Co Wealth Management Limited | Professional & scientific | 2024 |
| J & D Plumbing & Heating Limited | Construction | 2025 |
| J & R Food Plus Ltd | Wholesale & retail | 2018 |
| J & S Davis Limited | Wholesale & retail | 2012 |
| J & T Plumbing and Heating Ltd | Construction | 2023 |
| J a Accountancy Services Limited | Professional & scientific | 2023 |
| J and B Maintenance Ltd | Construction | 2021 |
| J and J Handyman & Gardens Limited | Other services | 2024 |
| J B Consultancy (London) Ltd | Administrative & support | 2013 |
| J C Flanagan Ltd | Real estate | 2023 |
| J Childs Management Services Limited | Professional & scientific | 2015 |
| J Collyer Services Limited | Construction | 2010 |
| J D Window & Door Repairs Ltd. | Construction | 2013 |
| J H Carpentry & Building Limited | Construction | 2016 |
| J Mason Holdings Limited | Financial services | 2020 |
| J S H Environmental LLP | | 2001 |
| J Szygula Limited | Health & social care | 2011 |
| J V Miller & Sons Ltd | Construction | 2025 |
| J W Developing Solutions Limited | Professional & scientific | 2013 |
| J W Flat Roofing Limited | Construction | 2025 |
| J W Joinery & Spraying Services Ltd | Construction | 2024 |